Electron beam induced current experiments in the planar geometry are performed on Mo/CuInX2/CdS/ZnO thin film solar cells where X is S, Se. We measure the collection efficiency of cells as a function of the beam energy and subsequently identify the depth dependent collection function. For CuInS2devices an effective diffusion length of 1.0±0.1 &mgr;m and a depletion layer of 0.05±0.03 &mgr;m is determined. The collection function of a CuInSe2cell points towards a low recombination rate at the back contact and a diffusion length exceeding 3 &mgr;m. ©1995 American Institute of Physics.